Radio communication systems that provide cellular and land mobile communication services are known in the art. Such systems comprise infrastructure equipment, which include equipment located at one or more sites, and subscriber units, which include portable and mobile communication units. Typically, a variety of equipment is required at each site. Such equipment includes radio base stations that support communication channels. A base station includes a receiver and a transmitter, where the transmitter uses one or more power amplifiers (“PAs”) to amplify the signal before transmission. This amplification generates a significant amount of heat during operation due to the internal components of the transmitter. In many cases, if left uncontrolled, the heat generated can permanently damage these internal components.
To maintain a desirable operating temperature of the transmitter, it can be cooled in a variety of ways. One widely used method is forced air cooling, where the heat generating devices of the transmitter are mounted on a heat sink that comprises a mass of thermally conductive material, such as aluminum. The heat sink typically includes a base member and a plurality of heat dissipating surfaces (or fins), either formed on the base member or bonded into grooves formed in the base member. Then forced air is provided by a fan located adjacent to the heat sink. The heat generated by the device is conducted to the heat sink, wherein the air flow from the fan dissipates the heat to the ambient air. Relative to other methods of cooling, such as liquid cooling, forced-air cooling offers an economical solution that is relatively easy to incorporate in the design and manufacture of a base station.
Power amplifiers can have varying power output levels depending upon the desired transmit power of the transmitter, and heat sinks may be constructed to handle these varying power output levels. The ability of a heat sink to dissipate heat, i.e., its power dissipation level, is proportional to its fin density (i.e., number of fins per inch), wherein heat sinks with a greater fin density have a higher power dissipation level. However the cost of a single casting tool, e.g., approximately $130,000, typically prohibits having multiple casting tools to manufacture heat sinks of varying power dissipation levels. Therefore, a single casting tool is typically used to accommodate the varying power levels of PAs. This is typically done in one of two ways.
First, a casting tool may be used to manufacture a heat sink having a fixed fin density, which can accommodate a maximum power dissipation level as a function of the number of fins per inch formed on the base member. The resultant heat sinks are then used across the board from low to high power applications. However, a shortcoming of this technique is its lack of flexibility. More specifically, low power PAs are burdened with the weight and cost of heat sinks having additional unneeded fins, and these additional unneeded fins cause higher back pressures in the air flow system, thus, requiring higher performance and more costly fans. Moreover, the casting process limits the fin density possible and, thus, the maximum power dissipation level possible for heat sinks used with the higher power PAs.
Alternatively, a casting tool may be used to manufacture a heat sink that has no fins formed on it, but that has a predetermined number of equidistant grooves formed in a base member. Fins may then be bonded into the grooves for causing the heat sink to have a power dissipation level that is a function of the number of fins bonded thereon. A shortcoming of this technique is that all of the fins must be bonded onto the base member by hand, which significantly increases the cost to manufacture heat sinks at any power dissipation level using this technique.
Thus, there exists a need for a heat sink architecture that has a predetermined number of fixed fins formed in the base member for a low power dissipation level and a predetermined number of grooves formed in the base member for bonding in additional fins for higher power dissipation levels, thereby, reducing tooling costs and the overall cost of manufacturing heat sinks over a range of power dissipation levels.